The present invention relates to a bore processing device for processing an inner surface of a bore of an object to be processed. More specifically, the present invention relates to a bore processing device for processing the bore of a high-accuracy bearing at high accuracy of cylindricity and surface roughness with plastic working, without a polishing process in which the bore is susceptible to flaws.
Recently, high-accuracy bearings rotatable at high speed are used in business machines and consumer equipment and it has become necessary to develop a hydrodynamic grooved bearing or a fluid bearing with higher accuracy.
For the finishing process in the plastic working of the bearing bore, there is a known method, called a pin sizing method, in which a pin is passed through the bore under pressure, and a known method, called a roller burnishing method, in which a roller is passed rotating through the bore as shown in FIGS. 5 to 7.
Referring to the drawings, one example of the known methods will be described hereinbelow. FIG. 5 is a cross-sectional view of a conventional bearing processing device. Reference numeral 11 denotes a roller guide having a plurality of guide grooves 11a in each of which a roller 12 is rotatably accommodated. A processing tool 14 of the device is composed of the rollers guide 11 and the roller 12. Reference numeral 13 denotes a sleeve of the bearing as an object to be processed.
The operation of the bearing bore processing device will be described hereinbelow.
Firstly, the sleeve 13 is set on a working table (not shown) and thereafter the processing tool 14 is downwardly moved in the bore of the sleeve 13 while rotating. At the time, since the processing tool 14 is designed to have the circle circumscribing the plurality of rollers 12 each of which has a diameter greater by a few micron meters or ten micron meters than the inner diameter of the bore of the sleeve 13, the rollers 12 pass through the bore of the sleeve 13 under pressure while the processing tool 14 is rotating with the rollers 12, thus causing plastic deformation in the sleeve 13 to obtain the necessary inner diameter and surface roughness of the bore of the sleeve.
However, the device has the following drawbacks: that is, in the plastic working process, as shown in FIG. 7, it is easy to deform at both the ends of the bore of the sleeve, and then the bore has a tendency to the cylindricity .delta. to gradually protrude at the center thereof and form a curved shape in cross-section. Additionally, when there is a variation within 20 micron meters in the inner diameter of the sleeve bore before a plastic working process, the bore has a variation within 10-15 micron meters in the inner diameter thereof after the plastic working process. Therefore, in a fluid bearing having a sleeve, there is much radial run-out and a variation in performance of sleeves made in quantity production.